A standard drill has a drive unit having a front end and an output shaft projecting from the front end and centered on and rotatable about an axis. A chuck body fixed on the shaft is formed with a rear end juxtaposed with the drive-unit front end, an axially forwardly open tool recess on the axis, and a plurality of angularly spaced and angled guides opening into the recess. Respective jaws displaceable in the guides have front ends in the recess. An adjustment sleeve rotatable about the axis on the body engages via formations such as screwthreads with the jaws for displacing the jaws radially on rotation of the sleeve about the axis. The shaft can also axially reciprocate or be provided with a reciprocating core shaft for hammer-drill action.
It is known, for example from commonly owned U.S. Pat. Nos. 4,607,855 and 4,627,628, to form the guides as outwardly opening holes so that any chips, oil drops, or the like that accumulate in the chuck can be thrown radially off, reducing fouling of the chuck mechanism. Nonetheless fine particles can build up and form a mechanism-clogging crust in the chuck. As a result the parts become unable to move freely relative to each other for self-tightening action or the like as described in commonly owned U.S. Pat. No. 5,286,041. The clamping force of the chuck is therefore reduced.
Hence commonly owned U.S. patent application 08/411,522 filed 28 Mar. 1995 describes a drill having a drive unit in turn having a front end and an output shaft projecting from the front end and centered on and rotatable about an axis, and a fan associated with the shaft for creating a moving stream of air traversing a location at the drive-unit front end. A chuck body fixed on the shaft is formed with a rear end juxtaposed with the drive-unit front end, an axially forwardly open tool recess on the axis, a plurality of angularly spaced and angled guides opening into the recess, and at least one passage extending between the chuck rear end and the recess. Respective jaws displaceable in the guides have front ends in the recess. An adjustment sleeve is rotatable about the axis on the body and interengaging formations on the sleeve and on the jaws displace the jaws radially on rotation of the sleeve about the axis. A deflector at the location directs the air stream into the passage for conducting the air stream through the recess so that any chips or the like in the recess will be entrained therefrom by the air stream.
Thus with this system the air stream keeps the interior of the chuck clear, either by blowing out or aspirating chips and grit, depending on the direction of the air stream. In fact the system can create a high-pressure zone inside the chuck so that chips and the like cannot settle therein but are effectively prevented from entering at all.
While these systems have some effectiveness in keeping the tool recess clear, they do not prevent dust and grit from getting into the guide passages for the jaws. Thus these passages can become crusty to the extent where rotation of the jaws about their axes becomes difficult or impossible. Such rotation is exploited in self-tightening drill systems. Thus the known systems could use some improvement.